The present invention relates to a control technology of a data bus for an artificial satellite load, which is used for data communication between devices which are loaded in artificial satellites, and for transmission and reception of a command and a telemetry data from a ground station for controlling artificial satellite control, and especially to a data bus control method for an artificial satellite load and a system thereof for making possible not only conventional fixed periodical and fixed length data communication but also non-periodical and variable length packet data communication.
A conventional artificial satellite data bus system will be explained by referring to FIG. 1.
In FIG. 1, in the conventional satellite data bus system, a telemetry data collected by means of a data bus control apparatus 1 from each of devices 31–3n loaded in satellites is time-divided and multiplexed by means of a pulse code modulation (PCM) system, and is transmitted to a ground station.
However, in this artificial satellite data bus system by means of the PCM frame system, there are the following tasks:
The first task is that, since specific telemetry of the devices 31–3n loaded in satellites is transmitted to a ground station by means of a specific fixed-time time slot which comes every fixed period, only fixed length (usually 8 bits) telemetry data can be transmitted.
The second task is that, since by means of the specific time slot the data bus control device 1 must always transmit the specific telemetry of the certain devices 31–3n loaded in satellites, all of transmission orders and timing should be determined prior to launch of a satellite, and accordingly, flexibility of communication is missing.
In interactive type communication between computers, there are many cases in which comparatively short information is exchanged and data processing is conducted. In these cases, since, in the conventional data bus system until a series of processing is completed, a transmission line is kept connected within a time period during which information is not actually sent, for example, within a time period during which a computer is operating, it provides disadvantage from a data bus band efficient utilization point of view.
As other data bus system, there is an ethernet system which is utilized so much in a local area network (LAN) on the ground, and according to this system, since a variable length packet can be irregularly output, it provides advantage from a data bus band efficient utilization and communication flexibility point of view, and however, since, at the same time, collision on the bus can occur because a plurality of nodes start communication, there is a possibility that a command and so forth which should be surely transmitted real time are erased, and accordingly, there are several tasks from a communication reliability point of view.